This invention relates in general to polymerization and in particular to charge injection polymerization.
Addition polymerization of polymerizable unsaturated organic compounds is accomplished in a variety of ways. The most common method for effecting the polymerization of unsaturated organic compounds, such as vinyl polymers or vinyl monomers, is to react them chemically in the presence of a peroxide catalyst at elevated temperatures. Polymerization is initiated by the thermal decomposition of the peroxide catalyst which provides a free radical. Thermal decomposition of an initiator has disadvantages in that heat is required and the rate of generation of free radicals cannot be closely controlled because of the heat capacity of the system.
Another method for effecting the polymerization of unsaturated compounds is by irradiation. Light of short enough wavelength, i.e., high enough energy per quantum can initiate polymerization directly. It is customary, however, to use a photochemical initiator to increase the rate of polymerization. Radiation induced polymerization has disadvantages in that it is much slower than thermally induced polymerization and requires high energy light sources, such as ultraviolet rays of the type emanating from sunlight or a carbon arc lamp.
Another method of polymerizing unsaturated organic compounds is through the use of electric discharge in which the monomer is polymerized by the discharge of electricity through monomer vapors. See, for example, U.S. Pat. No. 2,632,729 to Woodman. This system, however, requires that the monomer be a vapor at the operating temperature of the system or be vaporized before introduction into the system. High energy electrons are also used to cross-link polymeric solid materials, such as, polyethylene or polystyrene. This type of cross-linking, called curing, has beneficial effects on the mechanical properties of these polymers. However, this system requires a polymeric solid as a starting material and very high energy electron sources.
Liquid phase electric field polymerization of unsaturated organic compounds is also known in the art. For example, acrylonitrile, methyl methacrylate, vinyl acetate, and styrene can be polymerized by an electric field. Heretofore, however, the polymerizable materials had first to be dissolved in a solvent such as dimethyl-formamide containing a salt such as potassium nitrate or tetramethylammonium perchlorate to confer conductivity. See, for example, U.S. Pat. No. 3,193,475 to Baizer. Complex purification techniques are required to recover the product.